This invention relates to a printer having self-cleaning features and a print head for use in printers having a cleaning feature.
Ink jet printers produce images on a receiver by ejecting ink droplets onto the receiver in an imagewise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on a receiver medium such as a plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
Many types of ink jet printers have been developed. One form of ink jet printer is the xe2x80x9ccontinuousxe2x80x9d ink jet printer. Continuous ink jet printers generate a stream of ink droplets during printing. Certain droplets are permitted to strike a receiver medium while other droplets are diverted. In this way, the continuous ink jet printer can controllably define a flow of ink droplets onto the receiver medium to form an image. One type of continuous ink jet printer uses electrostatic charging tunnels that are placed close to the stream of ink droplets. Selected ones of the droplets are electrically charged by the charging tunnels. The charged droplets are deflected downstream by the presence of deflector plates that have a predetermined electric potential difference between them. A gutter may be used to intercept the charged droplets, while the uncharged droplets are free to strike the receiver.
Another type of ink jet printer is the xe2x80x9con demandxe2x80x9d ink jet printer. xe2x80x9cOn demandxe2x80x9d ink jet printers eject ink droplets only when needed to form the image. In one form of xe2x80x9con demandxe2x80x9d ink jet printer, a plurality of ink jet nozzles is provided and a pressurization actuator is provided for every nozzle. The pressurization actuators are used to produce the ink jet droplets. In this regard, either one of two types of actuators are commonly used: heat actuators and piezoelectric actuators. With respect to heat actuators, a heater is disposed in the ink jet nozzle and heats the ink. This causes a quantity of the ink to phase change into a gaseous bubble and raise the internal ink pressure sufficiently for an ink droplet to be expelled onto the recording medium.
With respect to piezoelectric actuators, a piezoelectric material is provided for every nozzle. The piezoelectric material possesses piezoelectric properties such that an applied electric field will produce a mechanical stress in the material. Some naturally occurring materials possessing these characteristics are quartz and tourmaline. The most commonly produced piezoelectric ceramics are lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate. When these materials are used in an ink jet print head, they apply mechanical stress upon the ink in the print head to cause an ink droplet to be ejected from the print head.
Inks for high speed ink jet printers, whether of the xe2x80x9ccontinuousxe2x80x9d or xe2x80x9con demandxe2x80x9d type, must have a number of special characteristics. For example, the inks should incorporate a nondrying characteristic, so that drying of ink in the ink ejection chamber is hindered or slowed to such a state that by occasional xe2x80x9cspittingxe2x80x9d of ink droplets, the cavities and corresponding orifices are kept open.
Moreover, the ink jet print head is exposed to the environment where the ink jet printing occurs. Thus, the previously mentioned orifices and print head surface are exposed to many kinds of airborne particulates. Particulate debris may accumulate on the print head surface surrounding the orifices and may accumulate in the orifices and chambers themselves. Also, ink may combine with such particulate debris to form an interference burr that blocks the orifice or that alters surface wetting to inhibit proper formation of the ink droplet. Of course, the particulate debris should be cleaned from the surface and orifice to restore proper droplet formation.
Ink jet print head cleaners are known. An ink jet print head cleaner is disclosed in U.S. Pat. No. 4,970,535 titled xe2x80x9cIn Jet Print Head Face Cleanerxe2x80x9d issued Nov. 13, 1990 in the name of James C. Oswald. This patent discloses an ink jet print head face cleaner that provides a controlled air passageway through an enclosure formed against the print head face. Air is directed through an inlet into a cavity in the enclosure. The air that enters the cavity is directed past ink jet apertures on the head face and out an outlet. A vacuum source is attached to the outlet to create a sub-atmospheric pressure in the cavity. A collection chamber and removable drawer are positioned below the outlet to facilitate disposal of removed ink. However, the use of heated air is not a particularly effective medium for removing dried particles from the print head surface. Also, the use of heated air may damage fragile electronic circuitry that may be present on the print head surface.
Cleaning systems that use a cleaning fluid such as an alcohol or other solvent have been found to be particularly effective. This is because the cleaning fluid helps to dissolve the ink and other contaminants that have dried to the surface of the print head. One way to use a cleaning fluid to clean a print head is known as wet wiping. In wet wiping, cleaning fluid is applied to the print head and a wiper is used to clean the cleaning fluid and contaminants from the print head. Examples of various wet wiping embodiments are found in Rotering et al. U.S. Pat. No. 5,914,734. Each of these embodiments uses a cleaning station to apply a metered amount of cleaning fluid to the print head and to wipe cleaning fluid and contaminants from the print head. However, wipers can damage the fragile electronic circuitry and Micro Electro-Mechanical Systems (MEMS) that may be present on the print head surface. Further, the wiper itself may leave contaminants on the surface of the print head that can obstruct the orifices.
Thus, it is preferred to clean the surface of a print head by applying a cleaning fluid to the print head, using the cleaning fluid to clean the print head and removing the cleaning fluid from the print head all without contact with the print head.
One ink jet print head cleaner that uses a solvent to clean portions of the print head in a non-contact manner is disclosed in commonly assigned U.S. Pat. No. 4,600,928 by Braun et al. This patent is directed to cleaning components within an ink jet print head of a continuous type. In Braun et al., an orifice plate is to form ink droplets. These ink droplets are charged and are passed by a catcher that is selectively charged to attract certain droplets. The droplets that are permitted to pass the catcher are permitted to strike a media During cleaning, a fluid meniscus of ink is statically supported along an axis that is generally normal to the orifice plate to form a meniscus between the charge plate, orifice plate and/or the catcher. This meniscus is ultrasonically excited to clean the orifice plate and charge plate and catcher. The ink from the meniscus is then ejected into a sump that is located at a cleaning station.
U.S. Pat. No. 5,574,485, to Anderson et al. describes a cleaning station for cleaning a print head by scanning a liquid wiper across the orifices of the print head. In Anderson, et al. the cleaning station comprises a cleaning fluid jet and a pair of vacuum orifices flanking the jet. During cleaning the jet is moved into a position that is proximate to the print head. The jet is separated from the print head by a distance, xe2x80x9ctxe2x80x9d. In Anderson et al., xe2x80x9ctxe2x80x9d is defined as being xe2x80x9cabout 10 milxe2x80x9d, 0.25 mm, or 250 microns. When the jet is so positioned, the jet defines a flow of a cleaning fluid at the print head. A meniscus bridge of cleaning fluid is formed between the print head and the jet. Anderson et al., teaches that the print head is cleaned by scanning this meniscus bridge along the surface of the print head and by agitating the meniscus bridge using an ultrasonic vibrator. Cleaning fluid and any entrained contaminants are removed from the surface by use of the vacuum suction through the vacuum orifices.
Thus, Braun et al. teaches that a print head can be cleaned in a non-contact manner using a static fluid meniscus and Anderson et al., teaches cleaning a print head using a meniscus that is scanned along the surface of a print head.
It will be recognized that it is often necessary to use mechanical force to clean contaminant that has dried to the surface of a print head or that is positioned within an ink jet orifice. Where a cleaning fluid is used to clean a print head in a non-contact fashion, the force used to remove debris from the print head and ink jet orifices comes from fluid pressure applied in the form of a flow of cleaning fluid. However, the prior art does not teach a self-cleaning printer or self-cleaning print head that uses a pressurized flow of cleaning fluid to apply force to remove contaminant from the print head.
Further, the prior art does not teach a non-contact method for containing a pressurized flow of a cleaning fluid within a defined flow path during cleaning.
Thus, what is needed is a self-cleaning printer and self-cleaning print head that use a pressurized flow of cleaning fluid to clean a print head and ink jet orifices defined on the print head. What is also needed is a self-cleaning printer and self-cleaning print head that provide a non-contact method for containing a pressurized flow of a cleaning fluid within a defined fluid flow path during cleaning.
The present invention resides in a self-cleaning printer with a print head having an orifice plate defining an ink jet orifice, a cleaning orifice and a drain orifice. The orifice plate further defines an outer surface between the orifices. A source of pressurized cleaning fluid is connected to the cleaning orifice and a fluid return is connected to the drain orifice for storing used cleaning fluid. A cleaning surface is disposed adjacent to and separate from the outer surface to define a capillary fluid flow path from the cleaning orifice across the ink jet orifice and to the drain orifice. During cleaning, the source of pressurized cleaning fluid discharges a flow of a cleaning fluid into the capillary fluid flow path and pressurized cleaning fluid from the capillary flow path passes through the drain orifice and into the fluid return.
The present invention also resides in a self-cleaning print head with a print head body having an orifice plate defining an ink jet orifice, a cleaning orifice and a drain orifice. The orifice plate further defines an outer surface between the orifices. A source of pressurized cleaning fluid is connected to the cleaning orifice and a fluid return is connected to the drain orifice for storing used cleaning fluid. A cleaning surface is disposed adjacent to and separate from the outer surface for forming a space between the cleaning member and the print head. During cleaning operations, the source of pressurized cleaning fluid discharges a flow of a cleaning fluid into the capillary flow path and pressurized cleaning fluid from the capillary fluid flow path passes through the drain orifice and into the fluid return.